1. Field of the Invention
The present invention generally relates to a toner for developing an electrostatic latent image formed on an image bearing body, such as a photoconductor drum, in an electrophotographic apparatus, electrostatic recording apparatus, electrostatic printing apparatus, and the like, and more particularly, to a toner featuring a charge control agent added thereto.
2. Description of the Related Art
In electrophotographic apparatuses, electrostatic recording apparatuses and electrostatic printing apparatuses and the like, various types of toners have conventionally been used for developing an electrostatic latent image formed on an image bearing body, such as a photoconductor drum and the like. It is a general practice in the art to allow such a toner to be adsorbed on an electrostatic latent image formed on the image bearing body thereby to develop the latent image into a toner image. The toner image thus formed on the image bearing body is transferred onto a copy sheet and then fixed thereon.
In order to produce a sharp image suffering no fog, a toner having a proper chargeability is required. It is further required that the toner should present little change in charge quantity over time and be insusceptible to environmental changes such as variations of humidity causing significant attenuation of the charge quantity or production of agglomeration of toner particles. For example, if the charge quantity of the toner decreases from an initial set value, an increased amount of toner particles is scattered from the developing device, thus contaminating the periphery of the developing device with toner particles or producing toner fogs all over a resultant image.
It is therefore a conventional practice in the art to add a charge control agent to the toner material for accomplishing a stabile chargeability thereof.
Recently, a demand exists for a charge control agent of a white or pale color having an excellent color reproducibility such as to meet the need of production of color images.
Unfortunately, most of the charge control agents, which are colorless, white or pale yellow in color and generally used for imparting negative charges to the toner particles, comprise compounds containing heavy metals, such as a complex or a salt of chromium. The heavy metals are not desirable in a safety standpoint. Hence, demand exists for a negative charge control agent free from a heavy metal.